Method of and apparatus for recording sound



June 2; 1925.

E. B. CRAFT ET AL METHOD OF AND APPARATUS FOR RECORDING SOUND Filed Nov. 28, 1919 hi e/WWO: Edward 55 Ckafl" I .f W/hH a/71.: y v 6 v Any Patented June 2, 1925.

' {UNITED STATES "1,540,317 PATENT OFFICE.

EDWARD B. CRAF'IL OI HACKENSACK, AND EDWIN H. COLPITTS, OF EAST ORANGE, NEW JERSEY, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF

NEW YORK, N. Y., A CORPORATION OF NEW YORK.:

METHOD OF: AND APPARATUS FOR RECORDING SOUND.

To all whom it may concern:

Be it known that we, EDWARD B. CRAFT, a citizen of the United States, and EDWIN H. Conrrr'rs, a subject of the King of Great Britain, residing at Hackensack, in the county of Bergen and State of New Jersey, and at EastOrange, in the count of Essex and State of New Jersey, respectively, have invented certain new and useful Improvements in Methods of and Apparatus for Recording Sound, of which the following is a full, clear, concise, and exact description." i

The invention relatesto a method of and apparatus for recording sound and more particularly to sounds produced by the human voice and various musical instruments. The invention has for its object the elimination of certain diflioulties heretofore encountered in sound recording.

In'making records for reproduction in the well known types of sound reproducing machines, it has been necessary to take great precautions, particularly with respect to the relative location of the artist and therecording mechanism, and to employ artists who are specially trained in record making in order to obtain a record which will reproduce sound with any degree of faithfulness. Thus it has been comm'onfor the artist in .the case of a voice record to sing or talk into a horn or' mouthpiece and to vary the separation of artist and horn to obtain the desired tonal effects. In the case of instrumental music or in the case of duets or an ensemble of singers, great care has been necessary in grouping the singers or artists relative to the recording point in order to obtain the desired result. In view of the diificulty of training artists and also in view of the difficulty of grouping a large number of instruments for efiicient recordmg, it has been proposed to intercept or pick up the sound waves at a plurality of points and conduct them either acoustically or electrically to a common recording point.

regardless of the carewhich may be exercised, the sound wave ener reaches the various receivers at dlfierent t mes, and consequently when'the wave energy is transmitted to the recording point, that intercepted by the various sound receivers are not' in phase, which causes a disagreeable effect in the record which reproduces as an effect somewhat similar to an echo, In fact,

,this particular defect is often referred to as the echo effect and is caused by a difference in phase of effects produced by the same sound wave on the same record. When a large number of instruments are used for recording or where there is a soloist and an accompanist, it is of advantage to place the soloist and aceompanist at different points in a room or auditorium and to control the relative tonal values of the soloist and the accompanist or, in the case of an orchestra, of the various instruments. This may be done as indicated in a copending application, of' Harry B. Weir, Ser. No.

317,410, filed Aug. 14, 1919, by .placing the accurate time keeping between the artists inorder .to avoid the so-called echo effect since neitherartist hears the effect produced by f the. other.

In accordance with the present invention, however, the artist or group of artists, may enter a room-in which there is disposed at a plurality of difierent points anumber of sound receivers, and theperformanee may take place identically as though the performers were appearing before an audience without regard to any special procedure occasioned by the making of the record. Since all of the sound receivers will be effected by all of i the instruments and as no special precaution is taken to lace the instrument or the soloist an equa distance from, the receiving points, the invention provides for operating upon the wave energy bet-ween the point of interception'or reception and the recording point to compensate for differences in phase or differences in time of arrival of the particular sound wave energy at the various receiving'points. Although JthlS compensation may be accomplished acoustically byv varying the length of.air

path between the receiving and recording points, it can be more conveniently done by converting the .Wave energy into electrical waves in electrical circuits and operating upon the electricalwaves to bring them into p ase in a commofi circuit where they may be combined to cause the operation of an will more clearly appear from the following descri tion and the accompanying drawing, in WlllCh the figureshows. diagrammatically a recording system forming one embodiment of the invention. That part of the apparatus to the left of the' dotted line on the drawing may be located in an ordinary room or in an. auditorium. Theo art to the right of the dotted line will or inarily be grouped at some convenient point near the recording point so as to be under the control of a single operator.

There is provided in the room or aud torium a plurality of sound receivers or detectors indicated at 1, 2 and3. These may be spaced at various points about the room or, in the case of an'auditorium, they may be spaced at various points in the auditorium. Preferably they are located so that they will intercept the sound waves wlth chiciency regardless of the particular position in which the artist or artists instrument 4 may face. Although only three of these sound receivers are shown, it will be understood that ordinarily a greater number will be used as may be determined by the size of the room or auditorium. These sound receivers may be of any well known type in which the motion of a diaphragm or other sound responsive body is converted into -'filed December 24, 1917, Serial No. 208,661

variations of an electricalcircuit. The ty which it is preferred to use because of t e. high quality of its production, is that disclosed in an application of I. B. Crandall,-

issued as Patent 1,456,538. Each sound receiver is connected in circuitv with a source of electrical potential indicated at 4, 5 and 6 respectively. The circuit including these sources of potential is connected by means of transformers or the ordinary telephone repeating coils indicated at 7, 8 and 9 respectively, to a local circuit includin'gin series inductances 10, 11 and 12 and c'a-' pacities .13, 14 and 15 respectively. This local circuit when the inductances and capacities are properly selected functions as n varied at an electrical wave filter in the manner described in a patent granted to G. A. Campbell, No. 1,227,113, on May 22, 1917. These filters may be arranged to pass only electrical waves of a frequency within the range that it is desired to record so that noises due to movements of the performer or apparatus in the room, which are generally of very low frequenc may be eliminated. It is also possible to e iminate by'this. means certain tones produced by resonance of various parts of the apparatus or musical instruments when subjected to vibrations in the (produced by the regulated. The output circuit of the device includes a source of potential 29, a retard coil 30 and a condenser .31,-- the purpose'of which 'is well known in the art and need not be described here.

The output circuit of each amplifier is connected bymeans of transformer 32, 33 and 34 with adjustable artificial lines 35, 36 and 37, which are in turn inductively connectedby means of transformers 38, 39 and 40 with a common circuit including an electromagnet 41 which operates a stylus 42 to cut a record faceon the record surface 43. The artificial lines are of well known construction which have reviously been used, particularly in the te ephone art, for the purpose of simulatin a length of telephone transmission line. ey are adjustable so that the 135th of line simulated may be I It is well known that an electrical wave in passing over a transmission line is retarded by an amount which is a function either of the actual or simulated length of the 'line. It is desirable wheretones other than are tones are transmitted over a transmission line .that the retardation of such tone, or the electrical imcuits of the amplifier are repeating coils 44,

45 and 46 with any one of which the tele-' phone receiver 47 may be associated by means of the switch 48. The receiver 47 may also be associated with a transformer 49 coupling the common recording circuit with thereceiver by means of the switch 48.

The operation of making a record may jnow be described. The artist or artists merely enter the room or auditorium in which the sound receivers 1, 2 and 3 are located and without regard to the recording apparatus, proceed with their performance.

Sounds produced by an instrument or by' the voice, sav' at a point marked A on the drawing, wi-l reach the receiver 1- before reaching the receiver 2' and will reach receiver 3 after reachin receiver- 2. Thus the electrical impulses wi 1 be generated by the receiver 1 before a corresponding impulse is generated by the receivers 2 and 3. These impulses pass throu hthe filters 10, 11 and 12 where undesirab e frequencies are'eliminated, and thence by the transmission lines 16, 17 and 18 through the amplifiers 22, 23 and 24 to the artificial lines 35, 36 and 37 respectively. It will be noted, however, that the artificial line is adjusted to include a larger number of sections of artificial line than the lines 36 and 37 and consequently retards the wave transmitted through it to a greater degree than the corresponding waves transmitted-over line's'36 and 37. Of

- course, this relative adjustment will depend upon the position of the performer or performers relative to the position of the various sound receivers and will ordinarily be made bya conductor or operator who, by means of the switch 48, can connect his-telephone 47 to the common circuit and readily determine by the effect heard in the common circuit whether'the various artificial lines have received the proper adjustment to bring the energy transmitted over the associated transmission lines into exact phase coincidence. The operator may also listen in on any of the .individual circuits to make any adjustment ofthe amplification which he may consider necessary. T

It is therefore apparent that regardless of the relative position of the sound receivers and of the performer or performers or of the movements of the performers which might alter such relative position, the differences in time of arrival of the'same sound impulse at the intercepted or receiving point may be accurately compensated for, and brought into phase coincidence at the recordingpoint with the very much to be desired result of a natural and faithful record without requiring any restriction or special training upon part of the erformers.

In the embodiment of t e invention dis- "closed, which is the most eflicient embodiment of which the inventors are aware, the

sound wave energy is transmitted from the intercepting-or receiving points to the recording point in the form of electrical waves,

recording point in other forms without debut it is obvious thatwave' energy might also be transn'iitted from the intercepting to the parting from the spirit of the invention.

For example, the wave energy might be transmitted from the intercepting to the recording point, mechanically, instead of electrically, by means of a column of air as in the common speaking tube or stethoscope, or by means of a mechanical connection or Wire as in the mechanical telephone. In

either case, it will be possible to alter the effective length of the conducting paths, and consequently 'to compensate for differences in time of arrival of the wave energy at the receiving or intercepting points. A compensating device ,suitable for adjusting the of the sound waves at the intercepting points,

combining the electrical energy from the different points, andrecording the effect of the combined energy..

2.'Amet hod of recording sound which consists in intercepting sound-waves at a lUO plurality of separated points, converting said sound waves, into electrical energy at said points, conducting said energy. to a common point, retarding the electrical energy due to the earlier intercepted sound wave to bring it into phase coincidence with the electrical energy due .to the later interception of the same sound wave, combining the combined electrical'energ at a common point and recording the e ect of said combined ener 3% method of recording sound which consists-in intercepting sound waves at a plurality of separated points, converting said sound waves into electrical energy, compensating said electrical energy for differences in time. of arrival of said sound waves at the intercepting points, combining the eflects of said electrical energy, and recording the combined effects.

4; A method of recording sound which consists in intercepting sound-waves at spaced points, converting said sound waves into electrical waves, operating upon the phase of the electrical waves to compensate for differences in the time of arrival of the sound atthe intercepting points, combinin'g said compensated waves and utilizing the combined waves to control the making of a record.

' device and recording device, and means com- 5Q A method of recording sound which con s1sts 1n intercepting sound waves at a plurality of spaced points, converting said sound waves into electrical waves, collecting said electricalwaves intoa common circuit, converting said electrical waves i-nto audible effects for purposes of observation, adjusting the relative phase of the individual electrical waves until the desired combined effect a is secured, and recording the effect of said combined waves.

6. In combination, sound receivers inclnd ing means for converting sound waves into electrical waves, a recording device, con:

ducting paths each connecting a respective prising an artificial line for adjusting the effective electrical length of said transmission line.

8. In combination, a plurality of'soun'd receivers, a sound recording device, conducting paths from said sound receivers to said sound recording device, and means for relatively adjusting the effective length of said conducting paths. A 9. In'combination, a plurality of spaced.

devices for converting sound waves into elecirical waves, a corresponding plurality of ransmission lines, a commoncircuit with which said; transmission lines are cpupled, a recording device in said common circuit, and artificial lines included in said transmission lines to adjust the phase of the waves transmitted thereover. I N

10. In combination, a plurality of spaced devices for converting sound waves into electrical waves, a corresponding plurality of transmission lines, a common circuit with which said transmission lines are coupled, arecording device included in said common circuit, and artificial lines to bring the electrical waves transmitted over said transmission li'nes into phase coincidence before they are impressed upon said common circuit. g V

11. A system for recording sound comprising a plurality of devices for intercepting sound .waves at a plurality of spaced points, means for converting said sound waves. into electrical impulses, means for conducting said electrical impulses to a common recording point, means for compensating for differences in time of interception of said sound waves at the intercepting .points to bring said electrical impulses into phase coincidence at the common point,

and means for combining and recording the effects of said electrical impulses.

-.12. In combination, a source of sound, a plurality of spaced sound recelvers for convert-ing'the sounds from said source intoelectrical impulses, a transmission line for each of said sound receivers, means 111 each of said llnes for varying the efiectlve lengths thereof, a circuit common to said transmission lines and electrically coupled thereto, and a recording device in said common circuit. a

13. In combination, a source of sound,- a plurality of spaced sound receivers for converting sounds from said source into electrical impulses, a transmission line for each of said sound receivers, an adjustable, artiv ficial line in each of said lines for varying the effective lengths thereof, a circuit common to said transmission lines and electrical- 1y coupled thereto, and a. recording device in said commoncircuit,

In witness whereof, we hereunto subscribe our names this 25th 'day of November, A. D.- 1919.

EDWARD B. CRAFT. EDWIN H. COLPITTS. 

